The purpose of this work is to elucidate the physiology of the nexus. Experiments are designed to test the aqueous channel hypothesis for the nexus and to describe the molecular structure of the nexal membrane channel as it relates to the function of the junction. The diffusion of tracer molecules is monitored across the nexus with a variety of methods. The relationship of nexal membrane permeability vs. molecular size, charge and lipid solubility has been demonstrated. In addition, it is hoped that molecules will be found which alter the nexal membrane permeability of other molecules by affecting or blocking the nexal transport system (channel or pore) by binding to suspected fixed charges within the nexus.